Effects of substrate temperatures on the characterization of magnesium fluoride thin films in deep-ultraviolet region

Abstract

As a low refractive index material widely used in coatings for deep-ultraviolet optical systems, magnesium fluoride (MgF2) films were prepared by electron beam evaporation at different substrate temperatures. The effects of the substrate temperatures on the optical properties in vacuum and in air, microstructures, and composition were investigated, as were the microstructures, their composition, and the relation between them. In vacuum, the substrate temperature directly affected the microstructures which dominated the packing density and inhomogeneity along the film thickness. When the films were exposed to air, the refractive index increased and a nonmonotonic change trend of the refractive index with substrate temperature was observed due to adsorbed water and magnesium oxide (MgO) formed in the film. While a moderate amount of MgO reduced absorption loss by decreasing vacancy defects, excessive MgO increased the absorption loss because of the high extinction coefficient of the oxide.

Design and fabrication of far ultraviolet filters based on π-multilayer technology in high-k materials

“…Similar phenomenon of Al/MgF 2 transmittance filters was reported by Bates and Bradley 13 . This change may be explained by absorption of water in MgF 2 layer 29 and slow continuing oxidation of Al films 13 . When Al is deposited, little oxygen still exists due to gas release from deposition materials although the base pressure of chamber is 1.3 × 10 −4 Pa, and reacts with Al films.…”

“…Moreover, formed oxide layers undergo gradual structural transformation from amorphous phase to crystalline one 28 . In addition, it is generally accepted that MgF 2 film should be deposited at a high substrate temperature 29 , and Al film should be prepared at room temperature. In order to obtain high reflectance of filters, we do not make the substrate heated.…”

Nickel fluoride as a surface activation agent for electroless nickel coating of anodized AA1050 aluminum alloy

“…The F1s peak signal at 684.95 eV suggests its presence in the form of nickel fluoride [31]. However, it is also likely that aluminum fluoride was present as suggested by the broad F1s peak is at 687.75 eV [32][33][34][35]. The presence of aluminum hydroxide [Al(OH) 3 ], nickel hydroxide [Ni(OH) 2 ], and aluminum fluoride (AlF 3 ) cannot be excluded as these are typical by-products of the deposition process which can be incorporated into the coating and seal the pores [23,25,36].…”

Reaction Mechanisms during Atomic Layer Deposition of AlF3 Using Al(CH3)3 and SF6 Plasma

“…Metal fluorides typically have a low refractive index (1.3–1.6) and a wide band gap (>10 eV), and due to these properties, they are widely used in optical devices. − Recently, metal fluorides, AlF 3 and LiF in particular, have also received considerable attention for application in Li-ion batteries, either as a protective layer on the electrodes or as an active electrode material. − Furthermore, metal fluorides are of interest as a catalyst for the synthesis of chlorofluorocarbons and hydrofluorocarbons and have been employed in photovoltaics, e.g., as an electron-selective contact. − A variety of methods have been used for the deposition of metal fluorides, including evaporation, ,, sputtering, − and ion-assisted deposition − as well as atomic layer deposition (ALD). − Since ALD is a chemical vapor deposition technique that relies on sequential and self-limiting surface reactions, it typically results in highly uniform and conformal ultrathin films. , These characteristics are often relevant for the aforementioned applications of metal fluorides. , ALD of metal fluorides has been reported using various co-reactants, such as NH 4 F, the volatile metal fluorides TaF 5 and TiF 4 , and HF. − , Moreover, Lee et al demonstrated the ALD of AlF 3 , ZrF 4 , MnF 2 , HfF 4 , MgF 2 , and ZnF 2 using HF from a HF–pyridine solution. , For the thermal ALD of AlF 3 using HF, it was proposed that the reaction occurs according to the following two reaction equations: In the precursor subcycle (eq ), the Al­(CH 3 ) 3 (trimethylaluminum, TMA) prec...…”